Rotary pump and the like



Feb. 23, 1932. R. SCHMIDT 1,846,692

' ROTARY PUMP AND THE LIKE Filed June's, 1950 5 Sheets-Sheet 1 INVENTOR fiada z; J/imidz- BY ATTORNEYE qm WM Feb. 23, 1932.

R; SCHMIDT ROTARY PUMP AND THE LIKE Filed fJune 1930 3 Sheets-Sheet 2 IN VbNTO/f xudalf stimidt gfl x W A TTORNE V5 Feb: 23, 1932.

R. SCHMIDT ROTARY PUMP AND THE LIKE Filed June 6, 1930 3 Sheets-Sheet 3 l N VETOR @f-dalf 504m falt- A TTQRNE Y5 RUDOLF SCHMIDT, OF VIENNA, AUSTRIA, ASSIGNOR TO PATIAG pump embodying Patented Feb. 23, 1932 UNITED STATES PATENT OFFICE PATENTVERWER- TUNGS- UND INDUSTRIE-AKTIENGESELLSGHAFT, OF VADUZ, LIECHTENSTEIN, A

CORPORATIQN OF LIECHTENSTEIN ROTARY PUMP AND THE LIKE Application filed June 6, 1930, Serial No. 459,554, and in Austria June 13, 1929.

My invention relates to devices, such as pumps and the like, of the type in which co-operating rotary pistons are employed in conjunction with a corresponding casing having inlet and outlet ports for the fluid.

The object of my'present inventionis to obtain a very the above indicated type, thus enabling them to operate at high speeds without any shocks or jars such as would result from a non-uniform rotation. For this purpose, I have devised a novel formation of the co-operating pistons, the peripheral outline of which is made such that the successive points of contact, or rather of closest approach, of the pistons will form a closed curve. In practice, I prefer not to employ actual contact between the co-operating pistons, but to leave a small space between them, relying on the thin film of fluid in said space to effect a seal sufiicient for practical purposes, and to prevent the frictional losses and wear which result when the surfaces are in contact. With my present invention, such space, or the distance remaining between the pistons at their point of greatest approachto each other, may be kept constant throughout the rotation of the pistons. The curve formed by points of closest approach will lie alternately on opposite sides of a line connecting the centers of the cooperating pistons, and such pistons will virtually roll upon each other, and at the point of contact or closest approach, the outline curves of the pistons will have a tangent incommon.

-Three satisfactory and preferred embodiments of my invention are shown in the accompanying drawings, in which Fig. 1 is a diagrammatic view illustrating how the outline or profile of the piston may be plotted; Fig. 2 is a transverse section showing a pistons according to a different form of my invention; Fig. 3 isa section on line 33 of Fig. 2; Fig. 4 is a section showing a pump casing in connection with pistons of the form illustrated by Fig. 1, but in a different position.

For the sake of convenience, the co-operating pistons have been represented as in actual contact; it will be understood, however,

uniform action in devices of that in practice I prefer to leave a small clearance between the-pistons at the point of closest approac At C I have indicated the casing, provided with an inlet I and an outlet 0, located at the junction of the two cylindrical chambers C, C in which the pistons P, P are mounted to rotate, said pistons being mounted on shafts S, S which are journaled centrally in said chambers and geared together, as shown in Fig. 3, at G, G. In the embodiments illustrated, the two pistons and the chambers in which they rotate are alike, as are also the gears G, G. One of the shafts, as S, may serve for transmitting rotation to or from the pistons, according as the device operates to propel fluid, or to be actuated by a current of fluid.

Each of the pistons, in the embodiment 1 the shafts S, S" respectively, minus the radius The arcs M N and A the same angular extent, lines AO'N and K O M are straight lines. Within certain limits governed by practical considerations, the rat'o of R to 1" may be assumed arbitrarily. The portions of the piston'outline which connect the two circular arcs are determined in such a manner as to conform to a rolling motion of one piston on the other. An example showing how these connecting pistons A M and K N may be plotted is given in Fig. 1.

Having assumed certain values for the radii R and r and for the angles A O K and M O N, we draw two pistons in positions in which the common inner tangent t to the two circles II and III (drawn with the radius 1' about the center 0 and 0 respectively) will connect the end point A of the are AK with the corresponding point A of the arc AK'. The point Z where the tangent t intersects the line 0 O (O'Z being equal to Z0 deter- K are shown as of that is to say, the

mines the end of the straight line portions A Z and A Z respectively of the piston outline. The tangents KZ and K'Z are equal to A Z and A Z. Points of the curved transition portions Z M and Z M are plotted as follows: Through the center 0' let us draw a radius OA at an'arbitrarily chosen angle (p to the line 0'0 At the end A of this radius we draw the tangent t to the circle II. The perpendicular Z D dropped from Z on said tangent will locate a point D of the curve X connecting the successive points of contactor closest approach of the two piston outlines during the rotation of the pistons.

In order to find the point of the outline of the piston P corresponding to the point D, we will assume this piston to be stationary. The entire relative movement of the two pistons P, P may then be considered as composed of a partial rotation of the piston P about the center 0 through the angle a (A O A) which brings the center 0 to the new position O and of a subsequent partial rota tion of the piston P about this new center 0 through the angle (p. This will shift the point A to the new position A, at an angle (,0 to the line 0 0 connecting the two centers. At A we draw the tangent t perpendicular to 0 A. On this tangent we measure off the distance A D equal to AD which gives us a point D of the outline of piston P, which point corresponds to the point of contact or closest approach indicated at D. On the outline of the piston P, D is the point conjugate to D. This point D is obtained simply by describing an arc of a circle with the radius 0 D about the center 0, D being the point of intersection of said are with the outline portion A Z of the piston P. This means that as the pistons roll on each other, with the piston P rotating clockwise, and the piston P contraclockwise, the points D D will come into contact, or approach each other to the minimum distance, at the point D. By assuming successively different values of (p, as large a number of points such as D. D D as desired can be determined, thus plotting the curve X and the curved connecting portions Z M and Z M. It will be seen that the point Z of the curve X is equidistant from O and O and on a straight line therewith.

After the pistons have rotated through the angle a+ p in the directions indicated by the arrows, the points A and M reach simultaneously a position 01 on the line 0 0 as indicated by the lower end of the curve X in Fig. 1. Fig. 4 shows the pistons P, P in an intermediate position in which the point of contact or of closest approach is at the point (Z of the curve X. During the time that the outline portion A K of the piston P rotates in registry with the outline portion M N of the piston P, the point of contact or maximum approach remains at d. Thereupon the portion K Z will rotate in registry with the portion N Z, in substantially the same manner as when the portions A Z and M. Z were in registry with each other, except that the point of contact or maximum approach will shift along the curve portion (ZD, cZ,Z in the direction from d to Z. Then follows a period during which the portions Z N and Z K co-operate with each other, and during this period the point of contact or maximum approach shifts along the portion Z d" of the curve X, the points N and K coming closest together at the point d. Thereupon the circular arc portions N M and K A will rotate in registry with each other, and during this period the point of maximum approach will remain at d". Finally, the further rotation of the pistons will bring the portions M Z and A Z into co-operative relation, with the point of maximum approach travelling on the curve X from the point d to the point Z, thus bringing the parts back to the original position shown in Fig. 1.

It will be obvious that the straight elements A Z and A Z project at the centers of rotation of the pistons the same angles as the curved elements Z M and Z M, that is, the angles A OZ, Z O M, A O Z and Z O M are all equal.

It will be seen that during the rotation of the pistons, the point of contact or of maximum approach will be alternately at opposite sides of the center line 0, 0 except at the three points d Z, cl", and the point of contact will travel along what may be termed a closed curve, since said point of contact (or rather of maximum approach) travels on the same curve X first in the direction (1, D, (Z, Z, d and then back in the opposite direction. At each point of contact or maximum approach, the outlines of the two pistons P, P

will conform to a true rolling motion, that is, they will always have a common tangent at such points.

Instead of determining the shape of the curved outline portions Z M, Z N, N Z and M Z graphically, as explained above, I may do this by a purely mathematical process. Let us draw 0 E perpendicular to Z D, so that E D will be equal to 7". Then, since the angle 0 Z E is equal to (p, and if we designate 0 Z as a, it follows from triangle 0' Z E that Z E is equal to n cos (p, and Z D is equal to n cos -r. Let us designate Z D as m. Since 0' Z is equal to Z 0 Considering then the triangle 0 Z D, we find that its side 0 D is equal to the radius 0 D which corresponds to the angle ([1, and that the'angle D Z O is equal to 180 From this it folows that O D"= /n +2nm cos +m Thus, for each arbitrarily assumed value of follows that go, We can calculate the corresponding value of the distance or radius R" such as O D", and determine-the shape of the curve conjugate to the straight outline portions K Z, A Z, K Z and A Z. Since a is a. constant, and m a variable depending solely on (p, it the variable radius 0 D or R"1s purely a function of (p.

It will be understood Fig. 1 represents the path of a point of said line of contact or of closest approach; said line of contact or of closest approach which as stated above is a common tangent to both piston outlines) is parallel to the piston axes O, 0 and therefore perpendicular to the plane of Fig. 1. Thus, the several common tangents representing successive positions of the line of contact or of closest approach, will be parallel to each other.

t is not essential to my invention that each piston engage, or rather come close to, the peripheral wall of its chamber C or C", at only one portion of the piston outline. Such a construction, shown in Figs. 1 and 4 may be termed a single-tooth piston. In practice, the single-tooth pistons sometimes present drawbacks, in that they reduce the permissible width of the inlet I and outlet 0, in view of the possibility that, in certain positions of the pistons, a direct path might be opened from the inlet to the outlet. Another objection to the single-tooth piston construction arises from its one-sided and therefore unbalanced character, which compels operation at comparatively low speeds, or else the provision of separate counter-balancing means. These drawbacks are avoided by employing pistons having an even number of teeth, for instance double-tooth pistons such as exemplified by Figs. 2 and 3. Here, I have shown two balanced pistons P of like shape, each having two teeth, the outermost portions p of the piston outlines being arcs of circles coming close to the walls of the working chambers C, C. The portions p of one piston co-operate at times with the inner (small radius) are portions 12 of the other piston. The piston outlines are completed by the connecting portions p". With this arrangement, relatively wide ports I, 0 may be used.

In Figs. 2 and 3, I have illustrated a construction for obtaining tight joints at the ends of the pistons; this construction is applicable to the pistons shown in Figs. 1 and 4. The piston P or P is provided at each end with a cylindrical projection P extending into corresponding sockets in the adjacent walls of the casing, with slits or clearancesleft as indicated at S S S S This affords axial joints S S sealed by the liquid flowing through the apparatus, and relieves the piston of any axial strains on the portion within the outline of the projections or flanges P, so that only the piston portion situated exthat the line X interiorly of these flanges (the upper and the lower portions of the piston P in Fig. 3) is subjected to axial strains. This is of particular importance when the piston shaft is journaled in ball bearings, as these are liable to bend under relatively slight axial strains, in which case the clearance between the end faces of the piston and the adjacent wall of the casing would be injuriously affected. If desired, the effect of axial thrusts may be further reduced by connecting the chambers at the piston ends, by equalizing channels such as indicated at B.

The particular manner devised by me for insuring the tightness of joints, as just described in connection with Fig. 3 constitutes a separate invention, and therefore has not been claimed in the present application.

I claim:

1. A fluid apparatus comprising a casing provided with an inlet and an outlet, and cooperating pistons mounted to rotate in said casing, the cross sectional outline of each piston consisting of arcs of circles of different radii and portions connecting such circular arcs, said connecting portions being shaped according to a rolling motion of one piston on the other, and being composed of straightline elements tangential to the arc of smaller radius, and curved elements interposed between said tangential elements and the arc of greater radius, thestraight-line elements of each piston cooperating with the curved elements of the other piston during rotation thereof.

2. A fluid apparatus comprising a casing provided with an inlet and an outlet, and cooperating pistons mounted to rotate in said casing, the cross sectional outline of each piston consisting of arcs of circles of different radii and portions connecting such circular arcs, said connecting portions being shaped according to a rolling motion of one piston on the other, and being composed of straightline elements forming portions of an inner tangent common to the smaller radius circles of both pistons, and curved elements interposed between said straight-line elements and the circular arc of greater radius, said curved elements of one piston cooperating with said straight-line elements of the other piston and being formed according to a rolling motion of one piston on the other, the straight-line elements of each piston cooperating with the curved elements of the other piston during rotation thereof.-

3. A fluid apparatus comprising a casing provided with an inlet and operating pistons mounted to rotate in said casing, the cross sectional outline of each piston consisting of arcs of circles of different radii and portions connecting such circular arcs, said connecting portions being shaped according to a rolling motion of one piston an outlet, and coon the other, and being composed of straightline elements tangential to the arc of smaller radius, and curved elements interposed between said tangential elements and the are of greater radius, the variable radii R of said curved elements conforming to the formula where n is equal to one-half of the sum of said greater radius It and said smaller radius 1', (p is the variable angle which the straight-line connecting the axial centers of the pistons forms with a line drawn from the median oint of said straight-line to the outer end of the radius B when in the position of contact or closest approach, and m is equal to 'n cos 1-, the straight-line elements of each piston cooperating with the curved elements of the other piston during rotation thereof.

4. A fluid apparatus comprising a casing provided with an inlet and an outlet, and cooperating pistons mounted to rotate in said casing, the cross sectional outline of each piston consisting of arcs of circles of different radii having equal central angles, and portions connecting said circular arcs, said connecting portions being shaped according to the rolling motion of one piston on the other, and being composed of straight-line elements connected to a circular arc of smaller radius and curved elements connecting said straight-line elements to a circular arc of larger radius, said straight-line and curved elements projecting equal angles at the axis of rotation of the piston, the straight-line elements of each piston cooperating with the curved elements of the other piston during rotation thereof.

5. A fluid apparatus comprising a casing provided with an inlet and an outlet, and cooperating pistons mounted to rotate in said casing, the cross sectional outline of each piston consisting of arcs of circles of different radii having equal central angles, the sides of which extend as continuations of one another through the center of rotation of the piston, and portions connecting said circular arcs, said connecting portions being shaped according to the rolling motion of one piston on the other, and being composed of straight- 'line elements connected to a circular arc of smaller radius and curved elements connecting said straight-line arc of larger radius, said straight-line and curved elements projecting equal angles at the axis of rotation of the piston, the straightline elements of each piston cooperating with the curved elements of the other piston during rotation thereof.

In testimony whereof I have hereunto set my hand. a RUDOLF SCHll/HDT.

elements to a circular 

